[sdiy] extreme pitch-shifting?

[Niels A. Moseley]

Hi gregory,

You're actually building a radio! There is no need to "sample", you just 
need an RF mixer. Something like the NE602 (or NE612, SA602, SA612) will 
do. It will go up to 200 MHz with the internal oscillator.

The mixer will move the frequency-of-interest (e.g. 100 MHz) down to the 
audio range. This will produce weird tones like a diode ring mixer. You 
can actually use a diode ring mixer as an RF mixer -- the NE602 contains 
a mixer made from transistors but the basic function is the same!

For the casual builder 2.4 GHz is really high and you need to use 
special circuits, components and RF circuitboards.

Probably the easiest thing you can do to get "on the air" is buy a cheap 
AM radio with lots of bands. AM demodulation is dull so to make it 
interesting, you need to inject a 455 kHz carrier (which is usually the 
final intermediate frequency of the radio). This sounds more complicated 
than it actually is.

You just build an oscillator that produces 455 kHz. It has to be rather 
stable so I suggest using a ceramic resonator. Take a look at 
http://hem.passagen.se/communication/ceramic.html . At the bottom of the 
page is a schematic diagram. You can use that to generate 455 kHz. (It 
could use some lowpass filtering at the output; otherwise you'll receive 
harmonics of the 455 kHz oscillator.)

After building the oscillator, attach a piece of wire to the output 
(like an antenna) and wind it around the radio. The 455 kHz RF signal is 
transmitted into the radio where, hopefully, it will intermodulate with 
the RF. Now you have single-sideband (SSB) reception. AM radio signals 
will squeel and you can receive all sorts of strange signals that you 
can't normally hear with an AM radio.

Hope this helps!

Regards,
Niels.

gregory zifcak wrote:
> hi all,
> i am wondering about the best way to pitch down rf signals into audio 
> range. i'm not trying to demodulate, just listen to say, 2.4 GHz noise 
> dropped to 1kHz. is my best bet super fast digital sampling and then 
> lowering the clock frequency? or is there some type of divide-down 
> scheme i could use (i'm guessing most rf noise is not squarewaves)?
> thanks for any suggestions.
> new to rf,
> greg
> 
> 
> .
>